On Mon, 03 Nov 2003 12:20:02 -0600, Cecil Moore
wrote:

|Wes Stewart wrote:
| On Mon, 03 Nov 2003 09:26:05 -0600, Cecil Moore
| wrote:
|
| |Roy Lewallen wrote:
| | If you could build an antenna from
| | straight conductors and lumped inductors, the result would be very close
| | to EZNEC's predictions.
| |
| |Hard to prove since lumped inductors are impossible in reality. Why
| |does EZNEC show so much difference between lumped inductors and stub
| |inductors?
|
| I see no such difference in my model.
|
|There shouldn't be a lot of difference. I have modeled two short dipoles,
|one loaded with a lumped inductive reactance and one modeled with the
|same reactance using an inductive stub. EZNEC reports the following:
|
| Inductance lumped j335 10'stub
|
|current in segment just before the coil .8374 amp .8384 amp
|
|current in segment just after the coil .7971 amp .5642 amp
|
|The relative difference just before the coil is quite small, 0.12%.
|
|The relative difference just after the coil is quite large, 41.28%.
|
|There just cannot be that amount of difference between a coil and a
|stub.

If you use the ideal transmission line model, there is *zero*
difference between an ideal inductor and a transmission line stub.

You are comparing a mess of wire with a ideal lumped inductor. Apples
and oranges.

If you really want to model this stuff accurately take a few hundred
$K out of your next retirement check and buy a high frequency
structure simulator.

www.hfss.com